Intracellular recording and HRP iontophoresis will be used to mark individual LGNd cells in the cat. We will thus obtain detailed structure/function relationships at the single cell and subcellular levels with both light and electron microscopy. We shall correlate ultrastructural features, including afferent and efferent terminals, to electrophysiological data. We shall first concentrate on A laminae X and Y relay cells, and also study PGN cells, MIN cells, and C laminae cells. We hope to gain insights into the morphological basis of LGNd functional circuitry for single neurons.